I. Field of the Invention
The present disclosure relates to silver loaded ion exchange resins for the removal of a halide from reactor effluent reaction product mixtures or product streams. In some aspects, the present disclosure provides a method of removing inorganic or organic iodides from an acetic acid process reactor or product stream.
II. Description of Related Art
Carbonylation processes often use transition metal catalysts and additives or promoters that contain halogens, typically iodide ions. For example, production methods for making glacial acetic acid may include lithium iodide and methyl iodide. Methyl iodide is often difficult to remove from carbonylation products. These halogen containing by-products or additives are passed along the process and can poison downstream process such as esterification or polymerization catalysts. For example, many of the catalysts used in the production of vinyl acetate are “poisoned” by iodide when it is present even at parts per billion (PPB) levels (please see U.S. Pat. No. 7,588,690; Jones, 2000; Haynes, 2010; and U.S. Pat. No. 5,139,981). As such, there is significant interest in methods and processes which reduce the amounts of these halogens, including processes where they may assist in carbonylation reaction(s).
One method of removing halides from a carbonylation reaction product is to pass the reactor effluent through an ion exchange resin with a cation. The cation, such as silver(I), binds the halide removing the halide from the effluent stream as described in U.S. Pat. No. 5,139,981. While U.S. Pat. No. 5,139,981 describes a wide array of silver loaded resins, traditionally, low levels of silver loading (i.e. loading of silver of less than 12%) are used because of cross reactivity of the resin with other carbonylation by-products or additives. Low levels of silver loading is typically utilized in order to maintain open sites for binding corrosion metals present in the reaction stream. Without sufficient open binding sites, the resin leaches silver ions from the resin to create the open binding sites to accommodate the corrosion metals. In particular, U.S. Pat. No. 5,139,981 notes that reaction products should be free from components such as corrosion metals, which can occupy empty binding sites or strip the loaded resin of silver(I). Higher iodide removal can be obtained at higher temperatures as described in U.S. Pat. No. 6,225,498, but higher temperatures detrimentally lead to thermal degradation of the resin and increased corrosion of the reactor. The increased corrosion further requires that the silver concentration be kept low in order to maintain open binding sites to bind the corrosion metals without displacing the bound silver.
Silver is an expensive starting material and the ion exchange resins used to remove iodide often preferentially bind protons or ions of corrosion metals such as iron, nickel, chromium and molybdenum over silver ions (please see U.S. Pat. No. 4,615,806). The removal of iron contaminants, a common by-product of the corrosion of the reactor, from glacial acetic acid was one of the first envisioned uses for the strong cation exchange resin Amberlyst™ 15 described in U.S. Pat. No. 4,615,806. If any of these types of ions are present, the silver on the silver loaded resin can be displaced for the higher binding metal and thus the ability of the resin to remove iodide is quickly eroded. The leaching of silver into the reaction mixture is a problem as noted in U.S. Pat. No. 5,801,279. Standard operational conditions likely lead to the leaching of the silver ions from the reactor bed; the inclusion of a downstream reactor bed to trap the entrained silver atoms is therefore recommended (U.S. Pat. No. 4,615,806). In an attempt to counter the reactivity of the resins to other corrosion metals, U.S. Pat. No. 5,220,058 replaces the sulfonic acid groups described in U.S. Pat. No. 5,139,981 with thiol groups, which are more resistant to metal exchange.
Methods have been undertaken to remove corrosive metals from reactor effluent to combat this problem. For instance, as described in U.S. Pat. No. 5,124,290 and WIPO Pat. App. Pub. No. WO 2005/107945, a first cation exchange resin may be used to remove the corrosion metals before the reaction effluent is further treated with a silver loaded resin. The introduction of an additional cation exchange resin bed increases the processing cost of purifying the reaction effluent. U.S. Pat. Nos. 6,642,168 and 6,657,078 highlight the importance of removing corrosion metals from the reaction mixture and utilizes two absorbent beds. In the first absorbent bed, the resin is not loaded with a metal that is reactive to halides so that corrosion metals can absorb selectively onto that bed and thus lower their concentration before entering the second metal containing bed. Additionally, in this method, the use of between 1 and 15 wt % is beneficial in the second metal containing bed as opposed to the 30-50 wt % disclosed in U.S. Pat. No. 5,139,981. Similarly, WIPO Pat. App. Pub. No. WO 2005/113479 treats the reaction effluent with a chelating agent, which removes the metal ions from the reaction. However, the chelating agents may bind the catalyst and promoter metals in lieu of binding the other corrosion metals and may not lower the concentration of the deleterious, corrosive metals. In addition, this method is not efficacious in preparing the reactor effluent for use of ion exchange resins to remove halides.
A need therefore exists for identifying methods which allow the use of high silver loaded resins to remove halides from a reactor effluent.